FIG. 1 is a simplified schematic of a sump system in a gas turbine engine. Items 3 represent a common oil-wetted chamber, called the bearing sump chamber or cavity, and items 6 represent a second, different common chamber, called the sump pressurization chamber.
Oil 9 is delivered by a nozzle 12 to a bearing 15 for lubrication and cooling. After usage by the bearing 15, the oil is gravity-drained to the bottom of in the sump chamber 3, and then evacuated by a scavenge system (not shown), as indicated by arrow 18. The scavenged oil is cooled, filtered, returned in oil stream 9.
Because of windage and splashing, some oil contained in the sump chamber 3 will ordinarily tend to leak into the sump pressurization chamber 6. To inhibit this leakage, various rotating seals 24, supported by a rotating shaft 27, isolate the sump chamber 3 from the pressurization chamber 6. Since the seals 24 do not perfectly block oil migration, airflow is generated across the seals 24 to further inhibit oil migration.
To generate this airflow, incoming air, represented by dashed arrow 30, pressurizes the pressurization chamber 6. This air is driven through the seals 24 by the positive pressure differential across the seals, as indicated by dashed arrows 33. This pressurization air velocity serves to keep splashing oil out of the seals 24 in the sump chamber 3, and to reduce its migration into the pressurization chamber 6.
The pressurization air, now present within the sump chamber 3, then exits through a sump vent 36, as indicated by dashed arrow 39, after passing through an air/oil separator (not shown).
The Inventors have observed that this approach is not necessarily optimal in modern gas turbine engines which are designed to produce larger thrusts than previously.